Dengue Fever

Description

Dengue fever and dengue hemorrhagic fever (DHF) are viral diseases transmitted by Aedes mosquitoes, usually Ae. aegypti. The four dengue viruses (DEN-1 through DEN-4) are immunologically related, but do not provide cross-protective immunity against each other.

Occurrence

Dengue, a rapidly expanding disease in most tropical and subtropical areas of the world, has become the most important arboviral disease of humans. More than 2.5 billion persons now live in areas at risk of infection, and an estimated 50 million-100 million cases of dengue fever occur each year, 200,000-500,000 of which are DHF. The case-fatality rate for DHF averages 5%. Epidemics caused by all four virus serotypes have become progressively more frequent and larger in the past 20 years. As of 2002, dengue fever is endemic in most tropical countries of the South Pacific, Asia, the Caribbean, the Americas, and Africa. Additionally, most tropical urban centers in these regions have multiple dengue virus serotypes co-circulating (hyperendemicity), which increases dengue transmission and the risk of DHF. Future dengue incidence in specific locales cannot be predicted accurately, but a high level of dengue transmission is anticipated in all tropical areas of the world for the indefinite future. The incidence of the severe disease, DHF, has increased dramatically in Southeast Asia, the South Pacific, and the American tropics in the past 20 years, with major epidemics occurring in many countries every 3-5 years. DHF is an emerging disease in the Americas. The first major epidemic occurred in Cuba in 1981, and a second major epidemic of DHF occurred in Venezuela in 1989 and 1990. Since then, outbreaks or sporadic cases, or both, of confirmed DHF have occurred in 28 tropical American countries. After an absence of 35 years, a small number of autochthonous cases of dengue fever have been documented in the continental United States (southern Texas in 1980, 1986, and 1995), associated with imported cases and epidemic dengue in adjacent states in Mexico. After an absence of 56 years, a limited outbreak of dengue fever occurred in Hawaii in 2001, associated with imported cases and epidemic dengue in the South Pacific.

Risk for Travelers

International travelers are at risk for dengue infection, especially if an epidemic is in progress. Cases of dengue are confirmed every year in travelers returning to the United States following visits to tropical and subtropical areas. Travelers to endemic and epidemic areas, therefore, should be advised to take precautions to avoid mosquito bites. The principal vector mosquito, Ae. aegypti, prefers to feed on humans during the daytime and most frequently is found in or near human habitations. There are two peak periods of biting activity, in the morning for several hours after daybreak and in the late afternoon for several hours before dark. The mosquito may feed at any time during the day, however, especially indoors, in shady areas, or when it is overcast. Mosquito breeding sites include artificial water containers such as discarded tires, uncovered barrels, buckets, flower vases or pots, cans, and cisterns.

Although not completely understood, current data suggest that, in addition to virus strain, the immune status (i.e., having had a previous dengue infection), age, and genetic background of the human host are the most important risk factors for developing DHF. In Asia, where herd immunity is high, DHF is observed most commonly in infants and children < 15 years of age who are experiencing a second dengue infection. In the Americas and the Pacific, where herd immunity is lower, it is more common to observe DHF in older children and adults. International travelers from nonendemic areas (such as the United States) are generally at low risk for DHF infection. There is little information in published reports about the risk of dengue infection in pregnant women. In spite of many epidemics, no increase in congenital malformations has been noted after dengue epidemics. A small number of recently reported cases suggests that if the mother is ill with dengue around the time of delivery, the child can be born with dengue or can acquire dengue through the delivery process itself.